Carbon nanotubes and nanowires are noted for their useful and novel properties in electrical, chemical, optical, and filtration applications, among others. Often, such nanotubes are grown in bulk and have non-uniform diameters. Accordingly, it would be desirable to provide methods for positioning and orienting nanotubes into arrays on a variety of substrates or within a variety of integrated devices. Existing efforts to align nanotubes for such applications are often difficult and labor intensive. Therefore, in situ efforts to align nanotubes during the growth process have been attempted.
In one such example, a porous substrate or filter is used to align the nanotubes as they are grown. In this example, the diameter of aligned carbon nanotubes and the density of the array are limited. Typically, very high temperatures are necessary to grow the carbon nanotubes. Accordingly, any substrates or other apparatus used to make a carbon nanotube array must be specially constructed to survive such high temperatures. Other issues arise with the difficulties of purifying and/or isolating nanotubes grown in an array based on certain characteristics, such as length or diameter.
Thus, a need exists for a method and apparatus for forming aligned, vertically or otherwise, carbon nanotubes at room temperatures on a variety of substrates where the carbon nanotubes can be purified and selected based on desired characteristics, such as length and/or diameter.